While not limited thereto, the present invention is particularly adapted for use as a fast breeder reactor duct and fuel rod cladding alloy. Such an alloy requires strong mechanical properties at high temperatures and at the same time must have both swelling resistance under the influence of irradiation and low neutron absorbence. Alloys such as those described in U.S. Pat. No. 3,046,108 to Eiselstein disclose age-hardenable nickel-chromium base alloys which have high strength and good ductility over a wide temperature range up to about 1400.degree. F. The aforesaid patent discloses a nickel-base alloy having a nominal composition consisting essentially of about 53% nickel, 19% chromium, 3% molybdenum, 5% niobium, 0.2% silicon, 0.2% manganese, 0.9% titanium, 0.45% aluminum, 0.04% carbon and the balance essentially iron. The alloy is characterized in the age-hardened condition by a yield strength (0.2% offset) of at least 100,000 pounds per square inch at room temperature and by a 100-hour rupture strength of at least 90,000 psi at 1200.degree. F.
It is known that nickel-base alloys containing titanium and aluminum, such as those described in U.S. Pat. No. 3,046,108, are strengthened by precipitation of a gamma-prime phase. It has also been found that by adjusting the amounts of titanium, aluminum and niobium in such alloys, a morphology can be obtained wherein precipitated gamma-prime particles are coated on their six faces with a shell of gamma-double prime precipitate. The resulting microstructure is very stable on prolonged aging and has good thermal stability characteristics.
In copending application Ser. No. 917,832, filed June 22, 1978, now U.S. Pat. No. 4,236,943 issued on Dec. 2, 1980 and assigned to the assignee of the present application, an iron-nickel-chromium alloy is described which incorporates the gamma-prime and gamma-double prime phases to achieve high strength mechanical properties at elevated temperatures as well as good swelling resistance in response to irradiation. The alloy described in the aforesaid copending application contains about 0.3% aluminum, about 1.7% titanium, about 45% nickel, about 10% chromium and about 1.7% niobium.